Demands on the controllability of friction clutches are very high in applications in the powertrain of a motor vehicle, both with respect to the precision of the setting of a specific torque and with respect to the speed or with respect to the delay-free response of the control in the engagement or release of the clutch. There is also the demand for intrinsic safety. This means that the most secure state (usually that is the released clutch) should be adopted automatically in the event of system failure.
A generic friction clutch is known, for example, from WO 2004/040158 A2. It has a controllable motor/pump unit as the pressure fluid source and a fast-opening valve as the valve. A fast release of the clutch is thus achieved. If this clutch or any other generic clutch should be engaged from the fully released position, the actuator must travel a specific path (the so-called “prestroke”) until the clutch beings to grip. The dead time passing in this context stands in the way of a fast and sensitive control of the clutch. This is even more the case since the clutch should have friction losses which are as small as possible in the disengaged state with a large speed difference between the two clutch halves. The prestroke, and thus the dead time, is then namely substantial.